Tissue ablation cannula and elecgtrode assembly that can be selectively operated with one or more active tips

ABSTRACT

An assembly ( 32 ) for use as part of an electrosurgical tool system ( 30 ). The assembly includes a cannula ( 42 ) and an electrode ( 66 ). The cannula is formed with a bend ( 54 ) proximal to the distal section. The electrode has a bent section ( 80 ) formed from a flexible shape memory material. The electrode can be inserted into the cannula so that a distal section of the electrode seats in the distal section of the cannula. In this configuration, the assembly has a single active tip, the distal section of the cannula. Alternatively, the electrode can be oriented so that when the electrode is inserted in the cannula the distal section of the electrode extends out of a side opening ( 58 ) of the cannula. In this configuration, the assembly has two active tips, the distal sections of both the cannula and the electrode.

BACKGROUND OF THE INVENTION

This invention generally relates to a cannula and electrode assemblyused for tissue ablation. The cannula and electrode assembly of thisinvention has plural conduct tips and be selectively operated so that atany given time a single tips or the plural tips are active.

BACKGROUND OF THE INVENTION

An electrosurgical tool system, often referred to as an electrosurgicalsystem, is a set of components used to flow current through a patient toaccomplish a specific medical procedure. Often the procedure is toablate at least some of the tissue through which the current is flowedto accomplish a desirable therapeutic effect. For example, anelectrosurgical procedure is sometimes performed to selectively removenerve tissue. This may be desirable if a set of the patient's nervescontinually transmit signals to the brain that inaccurately indicatethat a portion of the patient's body is in appreciable pain. If thereceipt of these pain signals adversely affects the quality of life forthe patient, an electrosurgical system is employed to ablate the nervesresponsible for the transmission of these signals. As a consequence ofthe tissue ablation process the nerve becomes a lesion. As a result ofthe nerve becoming a lesion, the nerve no longer transmits pain signalsto the brain.

Many electrosurgical systems include a cannula and electrode assembly.As implied by its name this assembly includes a cannula and anelectrode. The cannula is a needle like structure with sufficientstrength to puncture the skin of the patient and be positioned adjacentthe tissue through which the current is to be flowed. The distal end ortip of the cannula is conductive. The electrode is a closed end tubeformed of conductive material. The tube is designed to seat in the bore,the lumen, that extends through the cannula. Owing to the relativelysmall diameter of the electrode, often 0.4 mm or less in diameter, thistube tends to be relatively fragile. A hub or terminal is connected tothe proximal end of the electrode body.

When this type of assembly is used to remove tissue, the cannula istypically initially inserted into the patient and directed to a locationadjacent the target tissue, the tissue that is to be removed. During theinsertion process a stylet may be seated in the cannula lumen to providestructural strength to the cannula. Once the cannula is in the generallyvicinity of the target tissue, the stylet is removed. The electrode isinserted into the cannula lumen. A cable connects the electrode to acontrol console, also part of the electrosurgical system. The controlconsole functions as the power source that applies current to theelectrode. An electrically conductive ground pad, another component ofthe electrosurgical system, is placed against the patient. The groundpad is also connected to the control console.

The electrode assembly is used by sourcing a current from the controlconsole to the electrode. Since the electrode and cannula physicallyabut, there is current flow to the cannula. An electrical path isestablished through the patient from the electrode and sleeve section ofthe cannula to the ground pad. This current flow is densest through thetissue immediately adjacent the distal end of electrode and the exposeddistal end of the cannula. This current flow heats the tissue to atemperature that results in the ablation of the tissue.

Available cannula and electrode assemblies have proven to be goodinstruments for removing selected sections of tissue. Nevertheless, alimiting characteristic with the use of some of these assemblies isthat, when activated, they tend to ablate relatively small volumes oftissue, tissue having a volume of 0.8 cm³ or less. This is especiallytrue of assemblies having cannula with outer diameters of 18 gage ormore (1.25 mm or less.) There are procedures in which the practitionerwants to ablate larger sections of tissue than can be removed in asingle actuation of the assemblies. Consequently, after a first sectionof tissue is removed, the practitioner has to reposition the electrodeassembly to remove an adjacent section of tissue. This requires thepractitioner to, ever so slightly, reposition the electrode array sothat, in the next actuation, current is only flowed through the tissuethat is to be removed and not flowed through the adjacent tissue thatshould not be subjected to the removal process. Having to so repositionthe electrode assembly, in addition to requiring a significant amount ofskill, can lengthen the overall amount of time it takes to perform theprocedure.

An alternative cannula-and-electrode assembly has been proposed that isintended to increase the volume of tissue that can be removed with asingle placement of the cannula. Specifically, it has been proposed toform the cannula of this type of assembly with a side opening that islocated a short distance rearward of the distal end of the cannula. Theassembly is further constructed with a means to turn the electrode as itis inserted in the cannula so that the distal end tip of the electrodeextends out of this side port. The assembly thus has two tips: thedistal end tip of the cannula; and the distal end tip of the electrode.When current is sourced to the assembly, the current flows from thesetwo spaced apart tips.

Consequently, when current is sourced out of the electrode assembly ofthis invention, a relative dense electric field appears in the areaaround both of the tips. The field extend over a wider volume than thefield output by an assembly with a convention electrode-in-the distalend of the cannula construction. The electrode assembly of thisinvention thus outputs a relatively dense current flow through a volumelarger than is output by a conventionally constructed electrode assemblyof the same size.

There are procedures though in which the practitioner may not know untilafter the procedure is started if it is more appropriate to sourcecurrent through a one tip assembly or a two tip assembly. Similarly,during the procedure, the practitioner may want to initial apply currentusing first the one tip (or two tip) assembly and then switch toapplying current using a two tip (or one tip) assembly. In either of theabove situations, the practitioner may find it necessary to interruptthe procedure in order first remove one cathode and electrode assemblyand then insert a second assembly. As part of this process, thepractitioner needs to take the time to ensure that the second assemblyis properly positioned. Having to perform all these steps can increasethe complexity of the procedure and the tip it takes to perform theprocedure.

BACKGROUND OF THE INVENTION

This invention relates to a new and useful cannula and electrodeassembly for flowing current through living tissue. The assembly of thisinvention is designed so that after being inserted into the living beingthrough which the current is to be sourced the assembly can beconfigured to source current from a single tips or plural spaced aparttips. In many versions of the invention, the assembly can be set to havetwo active tips.

The cannula of this assembly is formed so as to have a bend immediatelyproximal to the distal end of the cannula. The cannula has an outletopening along the outer surface of the section of the cannula in whichthe bend is formed.

The electrode includes an elastic shaped section proximal to the distalend. More specifically, the electrode is shaped so as to have a lengthsubstantially equal to the length of the lumen that extends through thecannula. The electrode is further formed to have a bend in the sectionformed from elastic material. The bend is formed so as to be at the samegeneral location along the length of the electrode that the bend isformed in the cannula.

A hub is attached to the proximal end of the electrode. The hub isconnected to a cable through which current is sourced to the cannula. Inmany, but not all versions of the invention, the hub is provided with anindicia that provides an indication of the rotational orientation of theelectrode within the cannula.

The assembly of this invention is used by first inserting the cannula inthe patient. The cannula is positioned so the distal end tip is locatedadjacent the tissue through which the current is to be flowed. Theelectrode is then inserted in the cannula. If the practitioner onlywants to flow current out of a single tip, the tip of the cannula, theelectrode is inserted in the cannula in the rotational orientation sothat the bend in the electrode is in same orientation as the bend in thecannula. Consequently, when the electrode is seated in the cannula, thetip of the electrode is seated in the distal end of the lumen of thecannula. Current is therefore sourced only from the tip of the cannula.

Alternatively, the practitioner can configure the assembly of thisinvention so that current can be simultaneously sourced from two tips.The assembly is so positioned by setting the rotational orientation ofthe electrode so that it is out of orientation with the bend in thecannula. When the electrode, in this orientation, is inserted in thecannula, the distal end of the electrode will extend out of the sideport of the cannula. Thus while embedded in the patient, the assembly inthis configuration has two active tips; the cannula tip and theelectrode tip. As a consequence of the application of current to theelectrode, current is flowed from both tips through the adjacent tissue.

BACKGROUND OF THE INVENTION

The invention is pointed out with particularity in the claims. The aboveand further features and advantages of this invention are understood byreference to the following Detailed Description taken in conjunctionwith the accompanying drawings in which

FIG. 1 depicts an electrosurgical system with a cannula and electrodeassembly of this invention;

FIG. 2 is a plan view of the cannula and electrode assembly of thisinvention;

FIG. 3 is a cross sectional view of the cannula and electrode assemblyof FIG. 2;

FIG. 4 is plan view of the cannula of this invention;

FIG. 5 is plan view of the electrode of this invention;

FIG. 6A is a diagrammatic depiction of the alignment of the cannula andelectrode indicia of the assembly of this invention when the assembly isconfigured to source current from a single tip;

FIG. 6B is a cross sectional view of the assembly when the assembly isconfigured to source current from a single tip; and

FIG. 7A is a diagrammatic depiction of the alignment of the cannula andelectrode indicia of the assembly of this invention when the assembly isconfigured to source current from a single tip;

FIG. 7B is a partial cross sectional view of the assembly of thisinvention when the assembly is configured to source current from asingle tip;

FIG. 8 is a plan view of an alternative electrode of this invention.

DETAILED DESCRIPTION

FIG. 1 illustrates an electrosurgical system 30 including a cannula andelectrode assembly 32 of this invention. System 30 also includes aground pad 34 and a control console 36. Both the cannula and electrodeassembly 32 and ground pad 34 are connected to the control console 36.The control console 36 functions a power source that sources a currentfor flow between the cannula and electrode assembly 32 and the groundpad 34

The cannula and the cannula and electrode assembly 32, as seen in FIGS.2 and 3 includes a cannula 42 and an electrode 66. Electrode 66 isdisposed in the cannula 42. FIGS. 2 and 3 depict one operatingconfiguration of assembly 32, wherein the distal end tip of theelectrode 62 is located outside of the cannula 42.

Cannula 42, now described by reference to FIGS. 4 and 6B, includes a hub44. Hub 44 is formed from plastic or other electrically insulatingmaterial. (Cannula hub 44 and the above the below described electrodehub 68 of FIG. 1 are aesthetically different than the hubs depicted inthe other Figures.) Hub 44 is formed with a longitudinally extendingouter face 41. Face 41 is formed with indicia 43 best seen in FIGS. 6Aand 7A. In the depicted version of the invention, indicia 43 is shown astwo linearly aligned bars. The cannula hub 44 is formed to have athrough bore 46 that extends axially through the hub. Hub bore 46 isdimensioned to receive the body 74 of the electrode 62. The proximalportion of hub bore 46 is generally of constant diameter. (Here“proximal” is understood to mean towards the practitioner holdingassembly 32, away from the tissue to which the assembly 32 is applied.“Distal” is understood to mean towards the tissue to which assembly 32is applied, away from the practitioner.) Hub 44 is further shaped sothat, as bore 46 extends distally forward from the constant widthproximal section, the diameter of the bore decreases. At the most distalend of the hub 44, bore 46 has a diameter that allows the electrode body44 to slide through and out of the bore.

A cannula body 50 extends distally forward from hub 44. Cannula body 50is tube-shaped and formed from a flexible conductive material such asstainless steel. The cannula body 50 has opposed proximal and distalends, the proximal end being the end disposed in hub 44. In manyversions of the invention cannula body 50 is of size 18 gage or smaller(1.25 mm or less in outer diameter.) In still other versions of theinvention, cannula body is of size 20 gage or smaller (0.9 mm or less inouter diameter). Cannula body 50 has an axially extending lumen 52. Theproximal end of body 50 is mounted to the hub 44 so the proximal portionof lumen 52 is coaxial with hub bore 64. Lumen 52 extends from theproximal to the distal end of the body 50. Not identified is the distalend opening in the distal end of body 50 that opens into lumen 52. Insome versions of the invention the most proximal section of body 50,including the proximal end, is heat staked or adhesively secured incannula hub 44.

Cannula 42 is further constructed so that body 50 is not straight alongthe whole of the length of the body. In some versions of the invention,the body is shaped so the first 80% to 90% of the body that extendsforward from hub is linear in shape. Through this portion of the body,body lumen 52 is coaxial with hub bore 46. Forward of this linearsection, the cannula body is formed with a bend 54. Bend 54 has a radiusof curvature of 40 to 60 mm. Forward of bend 54, cannula body has adistal section, section 56. Cannula body distal section 56 is generallylinear in shape. The distal section has a length of approximately 5 to10 mm. The cannula body 50 is further formed to a side opening 58. Sideopening 58 is located on the side of the body that forms the outersurface of bend 54. The cannula body 50 is formed so that the lumen 52,in addition to extending through the proximal section of the body, alsoextends through bend 54 and distal section 56. Side opening 58 thusopens into the body lumen 52.

Cannula body 50 is further formed so that distal end is both open andhas a flared tip 60. More particularly the tip is flared so that themost distal portion of the body is a point forward of the inner side ofbend 54. The cannula 42 itself is constructed so that body 50 extendsforward from the hub 44 so that portion of the body forming the innersurface of bend 54 is directed towards the face 41 of the hub on whichindicia 43 is located.

A sleeve 64, seen only in FIG. 2, formed from electrically insulatingmaterial is disposed over the outer surface of the cannula body 50. Thesleeve 64 extends proximally rearward from a position slightly proximalto side opening 58. The sleeve 64 extends proximally so as to extendover the portion of the cannula that is disposed in hub 44.

The electrode 66, now described by reference to FIGS. 3, 5, 6A, 6B and7B, includes a hub 68 formed from plastic or other electricallyinsulating material. Hub 68 is formed to have two opposed faces 70 and75. Face 70 is formed with a first indicia 72, shown as “|”. The opposedhub face, face 75 is formed with a second indicia 76, shown as “\/”

A tube like body 74 formed of conductive material that has both flexibleand elastic characteristics extends forward from hub 68. Moreparticularly, the material is elastic so that, when subjected todeformative strain up to 3% and in some situations up to 6% deformativestrain from its initial shape, the body will not permanently deform andreturn to its initial shape. In one version of the invention, body 74 isformed from a nickel titanium alloy known as Nitinol. Body 74 has anoverall length such that when electrode 66 is inserted in the cannula 42so that the electrode hub 68 abuts cannula hub 44, the distal end tip ofthe electrode body is extends forward of at least a portion of the faceforming the flared tip 60 of the cannula body 50. The distal end tip ofthe electrode body does not extend beyond the distalmost end of thecannula body 50. In some versions of the invention, when the electrode66 is fully seated in the cannula 42, the distal end top of theelectrode body is located approximately 0.4 to 1.4 mm rearward of thedistalmost tip of the cannula body 50. The electrode body 74 has anouter diameter dimensioned so that when the electrode body 74 seats incannula lumen 54, there is contact between the inner surface of thecannula body 50 that defines lumen 54 and the outer surface of electrodebody 74.

Electrode body 74 is further designed to have a bend 80. In FIG. 5, thecurvature of bend 80 is exaggerated for purposes of illustration. Bend80 is located in the electrode body 74 so that when the electrode 66 isseated in the cannula 42, the electrode bend 80 seats in the section ofthe cannula lumen 52 defined by cannula bend 54. When the electrode 66is assembled, the body 74 is placed in a rotational orientation relativeto the hub 68 so that a distal section 82 of the body, the sectiondistal to bend 64, is directed towards hub face 70. It should be furtherunderstood that the distal end of body distal section 82 is the distalend tip of the electrode 66.

A thermocouple 84, represented by an oversized dot in FIGS. 6B and 7B isdisposed in the electrode body 80. Thermocouple 84 is disposed in thebody distal section 82. Insulated wires (not illustrated,) extend fromthe thermocouple 84 through the electrode body 75 to hub 68. Thestructure of the thermocouple 84 and the conductors that extend to thethermocouple are not part of the present invention.

A cable 92 (FIG. 1) extends proximally from the electrode hub 68. Thecable 68 contains a wire that, through the hub, is connected to theelectrode body 74. Also internal to the cable 92 are wires that connectto the wires internal to the electrode body 74 that are connected to thethermocouple 84. The proximal end of the cable 92 is connected to thecontrol console 36.

Control console 36 includes a power supply (not illustrated) capable ofsourcing a variable current to the electrode assembly 32. Ground pad 34functions as the return conductive terminal for the power source.Typically, the current is AC current. Control console 36 is configuredto allow the practitioner to adjust the frequency, current and voltagelevels of the sourced current. The specific structure of the controlconsole 36 is not part of the present invention. Features of controlconsoles that can be employed as control console 36 of system 30 thisinvention are disclosed in the incorporated by reference US Pat. Pubs.No. 2005/0267553 SYSTEM AND METHOD FOR CONTROLLING ELECTRICALSTIMULATION AND RADIOFREQUENCY OUTPUT FOR USE IN AN ELECTROSURGICALPROCEDURE published Dec. 1, 2005 and No. 2007/0016185, MEDICAL BIPOLARELECTRODE ASSEMBLY WITH A CANNULA HAVING A BIPOLAR ACTIVE TIP AND ASEPARATE SUPPLY ELECTRODE AND MEDICAL MONOPOLAR ELECTRODE ASSEMBLY WITHA CANNULA HAVING A MONOPOLAR ACTIVE TIP AND A SEPARATETEMPERATURE-TRANSDUCER POST published Jan. 18, 2007.

Electrosurgical system 30 of this invention is prepared for use byadhering the ground pad 34 to the patient. A cable 35 connects theground pad 34 to control console 36.

Cannula 42 is inserted into the patient adjacent the subcutaneous tissuethat is to be subjected to the ablation process. In the insertionprocess the flared distal end tip 60 of the cannula is the portion ofthe electrode assembly 32 that punctures the skin. In this step,electrode 66 is not fitted to the cannula 42. Instead, a flexible stylet(not illustrated) is seated in the cannula lumen 52. The stylet inhibitsthe cannula body 50 from bending to the extent that such bending resultsin the permanent deformation of the cannula.

The practitioner steers the cannula 42 so it is located in the vicinityof the target tissue, the tissue that is to be subject to the ablationprocedure. Owing to its relatively small diameter of the cannula body50, the cannula is relatively flexible. This flexibility facilitates theability of the practitioner to steer the cannula to the vicinity of thetarget tissue. As part of this steering process, the practitionerpositions the cannula so it is in the proper orientation relative to thetissue to be ablated. Once the cannula is properly positioned, thestylet is removed.

The practitioner then inserts the electrode 66 in the cannula 42. If theparticular procedure only requires the sourcing of current through asmall volume of tissue adjacent the distal end of the assembly 32, theelectrode is seated so as to position the distal section 82 of theelectrode body 74 in the cannula body distal section 56 as seen in FIG.6B. The practitioner so seats the electrode by setting the rotationorientation of the electrode body 74 inside the cannula body 50 so thatcannula and electrode bends 54 and 80, respectively, extend in the samedirection. The practitioner sets this orientation of the electrode byaligning the electrode hub 68 so that as the hub 68 is moved towardscannula hub 42, electrode indicia 72 faces cannula indicia 43 as seen inFIG. 6A.

As a consequence of the electrode 66 being so oriented, when the distalsection 84 of the electrode body approaches the cannula bend 54, theelectrode bend 80 causes the electrode distal section 82 to curve intothe cannula body distal section 56. At the end of this insertionprocess, the distal end tip of the electrode body 74 is depicted in FIG.6B, seated inside the distalmost portion of cannula lumen 52. When theassembly 50 is in this configuration, configuration, current is sourcefrom just one active tip, the insulation free portion of the cannulabody 50; bend 54 and distal section 56.

Alternatively, the practitioner may want to flow current through arelatively large volume of tissue adjacent the distal end of theassembly 32. To perform this type of procedure, the practitioner seatsthe electrode 66 so the distal section 82 extends out of cannula bodyside opening 58. Electrode 66 is so positioned by orientating theelectrode body in the cannula so that along the longitudinal axis of thecannula proximal section, the electrode bend 80 has an orientation thatis opposite to that of cannula bend 54. Electrode 66 is so oriented byrotating the electrode so electrode indicia 76 is placed in orientationwith cannula indicia 43 as seen in FIG. 7A. Once the electrode 66 is soorientated, the electrode body 74 is advanced through the cannula lumen52. Eventually the distal end tip of the electrode body 74 reachescannula side opening 58. Owing the elastic characteristics of thematerial forming the electrode body 74, the potential energy stored inbend 80 is released. This energy forces the body distal section 82 outof the cannula body side opening 58. When the electrode is fully seatedin the cannula, the distal section 82 of the electrode body 74 islocated outside of and adjacent to the cannula distal section 56 as seenin FIGS. 2, 3 and 7B.

When current is sourced through assembly as seen in FIG. 7B, the currentis thus sourced through two active tips; the exposed bend and distalsection of the cannula body and the exposed distal section 82 of theelectrode body. The current thus flows through a larger volume of tissueimmediately adjacent the cannula than when the assembly is configured tosource current from a single active tip.

The cannula and electrode of this assembly can thus be configured tooperate in one of two modes, a mode in which the assembly sourcescurrent out of a single active tip or a mode in which the assemblysources current out of plural active tips. This allows the practitionerto, by setting the mode of operating of the assembly, set if the currentis flowed through a relatively small volume or relative large volume oftissue adjacent the assembly 32.

Further, regardless of the mode of operation the electrode 66 istypically fully seated in the cannula 42. Consequently, regardless ofthe operating mode, the thermocouple 84 is spaced essentially the samedistance from tissue through which the current is flowed. The addedseparation of the thermocouple from the tissue when the electrode distalsection 56 of cannula body 50 is minimal. Thus, in either mode ofoperation, the signal output by the thermocouple 84 representative oftissue temperature, represents the actual temperature of the tissue withthe same degree of accuracy. This is useful because a practitioner maywant to set the control console to cause a current to be applied to thetissue that ensures that the tissue is heated to a specific temperature.When the system 30 is so configured, the control console 36 employs theoutput signal from the thermocouple as the signal representative oftissue temperature.

It is a still further feature of this invention is that, once thecannula 42 is inserted in the patient, the practitioner may reset themode of operation of the assembly 32. For example, the practitioner maystart the procedure by sourcing current from just the single active tip,cannula body distal section 56. The practitioner can then reset theassembly so that the current is formed from both tips. the cannula bodydistal section and the electrode body distal section. The practitionerperforms this switch by first partially withdrawing the electrode body74 from the cannula lumen 52. The electrode 66 is then rotated to placeelectrode indicia 76 is placed in registration of cannula indicia 43.The electrode body 74 is then fully reinserted in the cannula lumen 52.This rotation and reinsertion of the electrode body 74 results in theextension of the electrode body distal section out of the cannula bodyside opening 58. The assembly is then ready for operation in the mode inwhich the current is sourced from the two active tips.

Using the technique opposite from which is described above, assembly 32once fitted to the patient can be switch from the plural active tipoperating mode to the single active tip operating mode.

The above is directed to one specific version of the invention. Otherversions of the invention may have features different from what has beendescribed.

For example, there is no requirement that in all versions of theinvention a thermocouple be the component disposed in the electrode thatprovides a signal representative of temperature. A thermal resistor orother temperature sensitive transducer may perform this function.

Likewise there is no requirement that in all versions of the inventioneither the cannula body or electrode body be components formed out of asingle section of material. For example, the cannula body may include aproximal section formed from a non conductive plastic. The bend and thedistal section may be formed from metal or a other conductive material.

Further the described cannula is what is referred to as a monopolarcannula. The cannula has a single conductive surface. In an alternativeversion of this invention, the cannula may be a bipolar cannula. Thistype of cannula has two conductive surfaces that are electricallyinsulated from each other. The assembly of this version of the inventionis used to perform what is known as a bipolar ablation procedure. Thecannula second conductive surface functions as the return conductiveterminal.

In this version of the invention, when the assembly is operated in theplural active tip mode, the exposed distal section 82 of the electrode66 and one of the exposed sections of the cannula form a pair of commonactive tips. The second exposed section of the cannula serves as thereturn conductive terminal.

Likewise the electrode body may be formed from plural sections ofdifferent material. For example the electrode body may have a proximalsection formed from an elastic plastic. This plastic portion of theelectrode body may be formed with the flexible bend. Distal to bend, theelectrode may have a tip formed from a relatively inflexible conductor.An advantage of this version of the is that when the assembly isconfigured to operate in the plural active tip mode and the electrode isdeployed out of the cannula side opening, the relatively inflexibleexposed distal end may be less prone to breakage.

Further, there is no limitation that the invention solely be used inwhat are referred to as a monopolar procedure, a procedure in which theground pad functions as the return electrode. Assembly 32 of thisinvention may be used to perform what is referred to as a parallelbipolar ablation procedure. In this type of procedure two cannula andelectrode assemblies are inserted in the patient. These assemblies arepositioned on opposed sides of the tissue through which the current isto be flowed. In this type of procedure, the second cannula andelectrode assembly serves as what is referred to as the returnelectrode.

In these types of procedure, there is no requirement that both cannulaand electrode assemblies be of the type of this invention. In this typeof procedure it is recommended that the assembly 32 of this invention beorientated so that the electrode bend 80 is positioned so that theelectrode distal section 82 be directed towards the tissue through whichthe current is to be filed. This recommendation applies when theassembly 32 is operated either the single or active tip mode or theplural active tip mode. This orientation of the electrode 66 issuggested to ensure that the thermocouple 84 is positioned relativelyclose to the tissue through which the current is to be flowed. Thisincreases the extent to which the thermocouple outputs a signal that, asclosely as possible, represents the temperature of the tissue throughwhich the current is flowed.

FIG. 8 illustrates an alternative electrode 102 of this invention.Electrode 102 includes the same features of initially describedelectrode 66. The electrode 102 further includes a sleeve 104 formedfrom electrically insulating material that is disposed over theelectrode body 74. Sleeve 104 extends distally from hub 68 to a locationforward of the bend 80. In FIG. 8, the wall thickness of sleeve 104 isexaggerated for purposes of illustration.

The electrode of FIG. 8 is used in versions of this invention wherein aseparate set of conductors extends from cannula hub 44 to the controlconsole 36. These conductors (not illustrated) provide an electricalconnection between the control console 36 and the cannula body 50.

The cannula-and-electrode assembly of this invention can be thusoperated as either a monopolar unit or a stand alone bipolar unit. Theassembly is operated as a monopolar unit by seating electrode 102 incannula 44 so that the electrode body distal section 82 seats in cannulabody distal section 56. When the assembly is operated in this state,there is only a need to connect the electrode 102 to the control console36. The assembly in this state is operating with a single active tip;the insulation free portion of the electrode distal section 82. Groundpad 34 functions as the return terminal.

Alternatively, the practitioner may want to operate the assembly is astand alone bipolar unit. The assembly is so configured by orientatingelectrode 102 so that when the body is inserted in the cannula lumen 52,the electrode body distal section protrudes out of cannula side opening58. It should be understood that when the electrode 102 is sopositioned, the distal most portion of sleeve 104 also protrudes out ofthe cannula side opening 58. Thus when the assembly is so configured,the cannula body distal section 56 and the electrode body distal section82 are electrically insulated from each other. To operate the assemblyin this configuration, it is further necessary to connect the cable thatextends from the cannula hub 44 to the control console 36.

To operate the assembly in this configuration, current is flowed fromthe console power supply through the cannula, The exposed cannula bodydistal section 56, which is one of the active tip, functions as theactive tip. The exposed electrode body distal section 82 functions asthe return terminal. By so configuring the assembly of this invention,the practitioner can if desired, flow current through the small volumeof tissue that surrounds the exposed tips.

An alternative embodiment of this version of the invention can be formedby provide the cannula with a liner that extends around the interiorwall of the body that defines lumen 52. This linear also cover the outersurface of the cannula that defines side opening 52.

Accordingly, it is an object of the appended claims to cover all suchmodifications and variations that come within the true spirit and scopeof this invention.

What is claimed is:
 1. A cannula and electrode assembly including: acannula having a cannula body having: opposed proximal and distal ends;a distal section that is electrically conductive, the distal sectiondefining the distal end of the cannula body; a bend proximal to thecannula distal section; a lumen that extends distally and longitudinallyfrom the proximal end of the cannula body; and a side opening thatextends through a portion of the cannula body that defines an outerportion of the bend, the side opening opening into the cannula bodylumen; and an electrode adapted for connection to a cable that connectsthe electrode to a control console, the electrode having an electrodebody dimensioned to seat in the lumen of said cannula body, saidelectrode body having: a distal section formed from electricallyconductive material that is electrically connected to a conductorinternal to the cable and a section proximal to the distal sectionformed from elastic material, the section formed from elastic materialbeing located so that, when the electrode body is inserted in thecannula lumen, the section is within the section of the lumen defined bythe bend in said cannula body and the bend is shaped so that, dependingon the rotational orientation of the electrode body relative to thecannula body, when the electrode body is inserted in the cannula bodythe electrode body distal section either seats in the lumen portionwithin the cannula body distal section or extends out of the cannulabody side opening.
 2. The cannula and electrode assembly of claim 1,wherein said cannula and said electrode are formed with complementaryindicia that are arranged to provide an indication of the rotationalorientation of the electrode body relative to the cannula body.
 3. Thecannula and electrode assembly of claim 2, wherein: said cannula has ahub and said cannula indicia is disposed on the cannula hub; and theproximal end of said cannula body is mounted to the hub and the cannulabody extends distally from said hub.
 4. The cannula and electrodeassembly of claim 2, wherein: said electrode has a hub, said hub beingthe component of the electrode to which the cable is connected; saidelectrode body extends from said hub; and said electrode indicia aredisposed on the electrode hub.
 5. The cannula and electrode assembly ofclaim 1, wherein said cannula body is formed from a single piece ofmaterial.
 6. The cannula and electrode assembly of claim 1, wherein saidelectrode body is formed from a single piece of material.
 7. The cannulaand electrode assembly of claim 1, wherein the section of said electrodeformed from elastic material is formed from a nickel titanium alloy. 8.The cannula and electrode assembly of claim 1, wherein said electrodebody is in the form of a tube having a closed distal end.
 9. The cannulaand electrode assembly of claim 1, wherein an electrically insulatingsleeve is disposed over the cannula body, said sleeve extendingproximally from a location spaced proximally to the distal end of thecannula body.
 10. The cannula and electrode assembly of claim 1, furtherincluding a temperature sensor disposed in said electrode body.
 11. Thecannula and electrode assembly of claim 10, wherein said temperaturesensor is a thermocouple.
 12. The cannula and electrode assembly ofclaim 1, wherein said assembly is structured as a monopolar cannula andelectrode assembly.
 13. The cannula and electrode assembly of claim 1,wherein: said cannula has a hub; and the proximal end of said cannulabody is mounted to the hub and the cannula body extends distally fromsaid hub.
 14. The cannula and electrode assembly of claim 1, wherein:said electrode has a hub, said hub being the component of said electrodeto which the cable is connected; and said electrode body extends fromsaid hub.
 15. The cannula and electrode assembly of claim 1, whereinsaid electrode further includes a sleeve formed from insulating materialthat extends at least partially over said electrode body
 16. The cannulaand electrode assembly of claim 1, wherein the radius of curvature ofthe bend of said cannula is between 40 and 60 mm.
 17. A cannula andelectrode assembly, said assembly including: an electrode configured forconnection to a cable, said electrode including: a hub formedelectrically insulting material, said hub including opposed surfacesthereof indicia, the indicia on the opposed surfaces being differentfrom each other; and a body, said body having: a proximal section thatextends distally forward from said electrode hub; a distal sectionlocated forward of the proximal section, the distal section being formedfrom electrically conductive material and electrically connected to aconductor internal to the cable, the distal section defining an end ofthe body; and a bend located between the proximal and distal sections,so that as a result of the presence of the bend the proximal and distalsections of said electrode body are axially angularly offset from eachother; and a cannula, said cannula including: a hub formed fromelectrically insulting material and being formed with a bore forreceiving said body of said electrode, said cannula having a indicia;and a body, said body shaped to have: a proximal section that extendsfrom said cannula hub; a distal section located forward of the proximalsection, a bend that is located between the proximal and distal sectionsso that, as a result of the presence of said cannula body, the proximaland distal sections of the cannula body are axially angularly offsetfrom each other, a lumen that extends through the proximal section, thebend and distal section of said cannula body, the lumen dimensioned toreceive said electrode body and side opening in an outer surface of thebend, said side opening opening into the lumen that extends through thecannula body and wherein the bend and the side opening are formed in thecannula body so that: when the electrode body is inserted in firstrotational orientation within the cannula body to place a first one ofthe indicia on said electrode hub is registration with the indicia ofsaid cannula hub, the distal section of the electrode body seats in theportion of the cannula lumen disposed in the distal section of saidcannula body; and, when the electrode body is inserted in a secondrotational orientation to place a second one of the indicia of theelectrode hub in registration with the indicia of the cannula hub, thebend of the electrode body causes the distal section of the electrodebody to extend out through the side opening in said cannula body. 18.The cannula and electrode assembly of claim 17, wherein said electrodebody is formed from a single piece of material.
 19. The cannula andelectrode assembly of claim 17, wherein said assembly is structured as amonopolar cannula and electrode assembly.
 20. The cannula and electrodeassembly of claim 1, wherein the radius of curvature of the bend of saidcannula is between 40 and 60 mm.